Unrated Movie Icon

I am not sure if this is a skin feature or an XBMC feature, but I have a lot of movies that are either Unrated directors cuts or are classic movies from before the MPAA era, and want to see an icon that the movie is "UNRATED".

Is this something that can be incorporated with the skin or would this require a change to XBMC's library?

Currently, if a movie doesnt have a rating in the library, it just doesn't show an icon at all and I'd like to differentiate between movies that just didnt scrap the MPAA rating correctly and have it blank, as opposed to movies that are actrually Not Rated.